Individual study: The effect of shrub clearance in Mediterranean temporary pools on quillwort Isoetes setacea at Roque-Haute Natural Reserve, Languedoc-Roussillon, France
Rhazi M., Grillas P., Charpentier A. & Médial F. (2004) Experimental management of Mediterranean temporary pools for conservation of the rare quillwort Isoetes setacea. Biological Conservation, 118, 675-684
Mediterranean temporary pools are species-rich, containing many rare and endangered species. Land use changes, however, have resulted in invasion of pools by shrub and tree species. In this study, shrubs were experimentally removed from a temporary pool to determine the effect on a rare Mediterranean quillwort, Isoetes setacea. (See Case 351 for the additional effects of leaf litter removal or addition on I.setacea growth).
Study site & experimental design: One pool harboring quillwort Isoetes setacea was selected at Roque-Haute Natural Reserve in the province of Languedoc-Roussillon, southern France. The pool (surface area = 352 m²) was invaded mainly by elm Ulmus trees, and was shaded by shrubs from the surrounding arid shrubland. I.setacea was present but scattered in the pool. The pool was divided into two halves: a control zone (176 m²) and a cleared zone (160 m²). The cleared zone was cut in November 2000 using a chainsaw and a brush cutter. All cut material was removed but the leaf-litter was left.
The frequency of I.setacea was measured in May 2000 (pre-clearance) and May 2001 (post-clearance), in quadrats at 2 m intervals along eight permanent parallel transects, totaling 35 quadrats in the control zone and 42 quadrats in the cleared zone. The quadrats (0.3 x 0.3 m) were divided into nine squares (0.1 x 0.1 m) and the presence/absence of I.setacea was recorded in each, giving a frequency from 0 to 9.
In May 2000, I.setacea was located in 36 of the 77 quadrats, of which 13 were in the control zone and 23 in the zone that was to be cleared. The frequency of I.setacea was not significantly different between the two zones prior to the management work. After clearing, the frequency of I.setacea increased significantly in the cleared zone (May 2001, median 6.5) compared to the pre-clearance frequency (May 2000, median 2.5). Furthermore, there was a significantly higher frequency in the cleared zone than in the control zone (median = 0) in May 2001. Finally, in the control zone there was no significant difference in the frequency of I.setacea between May 2000 and May 2001.
Conclusions: Results from the Roque-Haute Natural Reserve suggest that scrub clearance is an effective management tool for increasing the density of I.setacea in Mediterranean temporal pools. Over what duration the benefits of scrub removal are on I.setacea populations is unknown, and presumably will vary from locality to locality.
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